In a point-to-point communication system, if the base station side can obtain Channel State Information (CSI), then it can optimize a modulation scheme, an encoding rate and a spatial distribution characteristic of signal power of a transmitted downlink signal to match the transmitted downlink signal with a channel propagation characteristic to thereby achieve the effects of enhancing the reliability of receiving the signal and of lowering the complexity requirement on a receiving algorithm, and particularly in a multi-user application scenario, the base station side can make a scheduling decision according to its obtained CSI to thereby improve the spectrum efficiency of the system and avoid inter-cell interference.
As currently specified in the Long-Term Evolution (LTE) Re1-8/9, an evolved Node B (eNB) can obtain CSI of a downlink channel according to channel reciprocity or a feedback from a User Equipment (UE), where a codebook-based implicit CSI feedback method is adopted for all of several general transmission modes of a Physical Downlink Shared Channel (PDSCH). In the foregoing protocol, it is specified that in Pre-coding Matrix Indicator (PMI) reporting modes of the transmission modes 4, 5, 6 and 8, the UE measures the downlink channel based upon a Cell-specific Reference Signal (CRS) and reports a Rank Indicator (RI) (which can be supported in the downlink to characterize the number of data streams) and a PMI to the eNB according to its own receiving process algorithm Further, the UE is required to report Channel Quality Information (CQI) of each codeword, where the UE shall calculate the CQI on the assumption that a locally recommended RI/PMI is adopted by the eNB.
As specified in the LTE Re1-8/9, the UE can be configured at an upper layer to report CSI periodically on a Physical Uplink Control Channel (PUCCH) and/or report CSI non-periodically on a Physical Uplink Shared Channel (PUSCH). Referring to Table 1, there are five PUSCH reporting modes for the PUSCH, and the UE adopts a PUSCH reporting mode configured semi-statically in network-side upper-layer signaling. Each PUSCH reporting mode corresponds to one or more PUSCH report types (i.e., CQI/PMI feedback types), and the UE creates corresponding CSI of a PUSCH report type corresponding to the PUSCH reporting mode specified at the network side, where the so-called CSI can be one or any combination of an RI, a PMI and CQI.
TABLE 1PMI Feedback TypeSingleMultipleNo PMIPMIPMIsPUSCH CQIWidebandMode 1-2Feedback(wideband CQI)TypeUE SelectedMode 2-0Mode 2-2(sub-band CQI)Higher Layer-configuredMode 3-0Mode 3-1(sub-band CQI)
However the existing PUSCH reporting mechanism in the LTE Re1-8/9 is designed for a single-codebook structure and focused on a single-user application scenario, and the PUSCH reporting mechanism will be further optimized in the Re1-10 (established for the LTE-A) to better support a multi-user scenario. As currently already established in the Rel-10, a dual codebook-based PUSCH reporting mechanism is adopted, and in this mechanism, CSI is divided into relatively stable long-term/wideband CSI and short-term/frequency-selective CSI with relatively highly time/frequency-selectivity, and a UE can quantize the two types of CSI with the use of two codebooks on a PUSCH in different feedback cycles.
However the existing single codebook-based CSI report mechanism does not distinguish between long-term/wideband CSI and short-term/frequency-selective CSI and thus is not suitable for the dual codebook-based PUSCH reporting mechanism specified in the Rel-10. Consequently it is desired to provide a new PUSCH reporting mechanism to report accurately long-term/wideband CSI and short-term/frequency-selective CSI.